The present invention relates generally to crash impact attenuators and more particularly to motor vehicle and highway barrier crash impact attenuators constructed from high molecular weight/high density polyethylene.
Motor vehicle related accidents are a major, worldwide health problem and constitute a great economic loss to society. For example, vehicular crashes kill more Americans between the ages of 1 and 34 than any other source of injury or disease. Put another way, for almost half the average life span, people are at greater risk of dying in a roadway crash than in any other way. In the U.S., more than 95 percent of all transportation deaths are motorway related, compared to 2 percent for rail and 2 percent for air. The yearly world wide societal costs of motorway deaths and injuries runs in the hundreds of billions of dollars. Indeed, the productive or potential years of life that are lost prior to age 65 as a result of motor vehicle related injuries or death are greater than those lost to cancer or heart disease.
Measures are being taken to reduce the billions of dollars lost in medical expenses, earnings, insurance claims, and litigation, as well as the intangible costs associated with human suffering. One important contribution to improved highway safety has been the development of impact attenuation devices which prevent errant vehicles from crashing into fixed object hazards that cannot be removed, relocated, or made breakaway. These devices have existed since the 1960's, and many technical improvements and innovative designs have been developed in the intervening years.
Today, such highway safety appurtenances as truck mounted attenuators, crash cushions, terminals, and longitudinal barriers are widely used and very effective. The employment of these devices has resulted in thousands of lives saved and serious injuries avoided over the last 25 years. Although a strong case can be made for the cost-effectiveness of highway safety appurtenances, the fact remains that their life cycle costs are high. A significant percentage of this total cost typically is associated with maintenance activities following vehicular impacts. This is the case because the vast majority of highway safety hardware dissipate energy through the use of sacrificial elements which must be discarded and replaced after an impact event.
In many instances, the initial installed cost of such hardware is small compared with recurring maintenance and refurbishment costs. Truck mounted attenuators, crash cushions, and terminals usually employ energy dissipating components which have almost no post-impact value and must be replaced at great expense. Similar problems with flexible longitudinal barriers have led to the increased use of the concrete safety barriers even though their installation cost per foot is significantly higher than beam-post systems.
There is another serious problem associated with damaged roadside hardware. In an alarming number of cases, the incapacitated safety device sits for days, weeks, or months before repairs are made. The potential safety and tort liability ramifications also translate into millions of dollars of lost revenue. It is clear that this money could be saved if all or most of our highway safety hardware were as maintenance-free as the concrete safety barriers. However, because of the need for controlled deceleration rates, impact attenuation devices cannot be composed of rigid concrete components. In fact, significant deformations are usually required of such devices.
The results of the efforts to design an effective crash impact attenuator have been the subject matter of several United States patents, including the following patents issued to the Applicant: U.S. Pat. Nos. 4,200,310 issued on Apr. 29, 1980, 4,645,375 issued on Feb. 24, 1987 and 5,011,326 issued on Apr. 30, 1991. Other efforts at creating effective crash impact attenuators include, among others, those inventions covered by U.S. Pat. Nos. 4,190,275 issued to Mileti, and 5,052,732 issued to Oplet et.al.
The patents issued to Applicant and identified above are based on the technology and concept of employing hollow cylinders connected together and aligned in a stacked relationship to absorb the impact of a crash between a car and a service vehicle or between a car and a roadside barrier. While these devices have been effective and have proven to be commercially successful, the expense of such devices has restricted their adoption and use in some areas to the full extent needed. Further, while the initial expense of construction or purchase and installation of such devices is significant, the acquisition and installation cost would be manageable in many jurisdictions if the cost of repair and replacement could be reduced. Repair and replacement costs cannot be budgeted with any precision because the number of crashes that will occur into a crash impact attenuator cannot be accurately predicted. However, once a crash with a crash impact attenuator occurs, the cylinders collapse in the course of absorption of the energy created by the crash. The collapsed cylinders must then be repaired or replaced. The cylinders can be repaired by beating them out into their original shape so that they will be available to accept the next crash or by replacing the cylinder within the system. In both instances, labor costs can be high and material costs are unpredictable. Such systems, when the cylinders are made from metal stock, which has been the case in the past, do not have regenerative properties and therefore the inability of such systems to regenerate themselves to the original condition is a substantial drawback to the ready acceptance of available crash impact attenuators. The safety that such systems provide and the ability to reduce the extent of injuries that result from crashes between an automobile and a service vehicle or an automobile and a roadside barrier could be greatly reduced if there was wide-spread use of the impact attenuation systems which I have developed.
What is needed then is a crash impact attenuation system which has regenerative properties so that it will regenerate itself to its original configuration and retain energy absorption capacity after being crashed into by a moving vehicle. Prior art devices that have a useful life greater than a single crash have included vinyl coated nylon fabric cylinders filled with water (see U.S. Pat. No. 4,583,716), plastic sheet having a honeycomb structure (see U.S. Pat. No. 4,190,275) which have some regenerative or multi-use characteristics but which fail to control the rate of deceleration upon crash in the effective manner of my impact attenuators, and others. The prior art does not include an expensive device or system which will dissipate the energy created by a crash and effectively attenuate the impact resulting upon a crash between a moving vehicle and a service vehicle or a moving vehicle and a roadside barrier yet which will regenerate itself and can be used over and over again without having to be replaced or repaired after each crash.
After extensive research and investigation over a number of years, I have determined that crash impact attenuation systems using the cylinder design of my prior U.S. Pat. Nos. 4,200,310, 4,645,375 and 5,011,326 as well as other designs employing cylinders as the primary dissipator of energy in such crash impact systems can be manufactured from high molecular weight/high density polyethylene which will provide a system that has regenerative properties and which can absorb multiple crashes without the necessity of any repair. Such systems, when manufactured of high molecular weight/high density polyethylene will regenerate themselves to their original or near original shape and strength after crash and collapse. The use of such materials in the construction of such systems of this nature is not suggested by the prior art and in fact the prior art teaches away from the use of materials such as high molecular weight/high density polyethylene in the cylinders of the systems because the prior art devices all call for metal, steel or alloy cylinders. Moreover, the high molecular weight/high density polyethylene cylinders have regenerative properties which I have discovered to be heretofore unknown because construction of such material have not been tested or used in applications of this nature.
The primary use of high molecular weight/high density polyethylene cylinders has been in the construction of pipe used in sewer systems and in fluid transmission lines. Such systems receive compressive pressures around the entire circumference of the pipe. The pipe is being pressured rather uniformly from the outside. To my knowledge, no tests have been conducted on the regenerative properties of such systems and such properties are unknown and undiscovered prior to my experimentations.